Dissertation presented for the degree of
Doctor of Philosophy in Engineering at the
University of Stellenbosch

en_ZA

dc.description.abstract

ENGLISH ABSTRACT: Planar weak link structures, such as micro-bridges, variable thickness bridges and nanobridges,
have always attracted a lot of attention. Their potential to behave as real Josephson
elements make them useful devices, with numerous applications.
Powerful techniques, such as focused ion-beam and electron-beam lithography, were successfully
used and are well understood in planar weak link structure fabrication. In this
dissertation the results of an experimental study on planar weak link structures are presented.
For the first time these structures have been successfully fabricated using AFM
nanolithography on hard high-temperature superconducting YBCO tracks, where diamond
coated silicon tips were used as a ploughing tool.
Superconducting YBCO thin films were deposited on different substrates, using inverted
cylindrical magnetron sputtering. The films were used to fabricate micro-bridges, variable
thickness bridges and nano-bridges, by using conventional photolithography, argon ion-beam
milling and AFM nanolithography.
The measured I-V characteristics of the fabricated micro-bridges (width down to 1.9 µm),
variable thickness bridges (thickness down to 15 nm) and nano-bridge (width down to 490
nm) showed well defined DC and AC Josephson effect characteristics.
For better understanding of the behaviour of these types of weak links, critical current versus
temperature measurements, and magnetic field modulation of the critical current measurements,
were also performed, with the results and discussions given inside the chapters.
The major challenges that were experienced in the laboratory during the fabrication processes
and the operation of the fabricated devices are also discussed, with the solutions given
where appropriate.